The present invention relates to a method of making a flanged tubular metallic part that is used, for example, as a housing of a gas sensor, by cold forging.
For optimizing the combustion efficiency of a combustor such as an automotive engine and boiler, it has been used a gas sensor for detecting the components such as oxygen contained in the exhaust gas emitted from the engine. Such a gas sensor includes a sensor element and a flanged tubular metallic part (i.e., housing) surrounding the sensor element. Such a metallic part is made of ferrite-system stainless steel and shaped so as to be entirely hollow cylindrical and include a hollow portion extending axially therethrough and an integral, outward hexagonal flange.
It is proposed to make such a flanged tubular metallic part by a cold forging process as shown in FIGS. 6A to 6D. As shown in FIG. 6A, a metallic blank 120 of stainless steel, having a cylindrical shape is prepared and is previously annealed and processed by lubrication treatment.
First, by using, though now shown a die assembly having a die, a double-acting punch and a counter punch, a tubular portion 125 having a deep axial hole 124 extending from an end surface 121 of the blank 120 and a hexagonal flange (bolt head) 126 extending outward from an outer circumferential surface 123 are formed at the same time as shown in FIG. 6B.
Then, by using, though not shown, another die assembly having a die, a punch and a counter punch, a deep hole 127 that is made deeper in the tubular portion 125 and a shallow hole 128 having an open end at the other end surface 122 are formed.
Finally, by perforating a wall between the deep hole 127 and the shallow hole 128 by means of a punch (not shown), a hollow portion 129 extending throughout between the end surfaces 121, 122 as shown in FIG. 6D is formed. Thus, a flanged tubular metallic part 130 is obtained (refer to Japanese patent provisional publication No. 8-52530).